The present invention relates to a test rig for testing a power transmission device and to a test system comprising such a test rig provided with a power transmission device.
Although not exclusively, said test rig is intended more particularly for testing a transmission gearbox (main, intermediate or tail transmission gearbox) of a helicopter.
It is known that a test rig is generally used for carrying out two types of test, namely:
development tests, the purpose of which is to simulate the actual operating conditions as faithfully as possible (particularly to simulate the rotor head loading pattern and the levels of load on a main transmission gearbox for a helicopter) of the power transmission device; and
acceptance tests, the purpose of which is to check the correct operation of the various mechanical parts, under a standard loading spectrum (measuring torque, rotational speeds and temperatures in particular).
In general, such a test rig for testing a power transmission device comprising at least an input shaft (drive shaft for example), an output shaft (rotor shaft for example) and a casing, comprises:
a first assembly comprising first coupling means and a coupling shaft (or transmission) which can be connected to the output shaft of the power transmission device that is to be tested, via said first coupling means;
a second assembly which can be connected to the input shaft of said power transmission device via second coupling means; and
in the case of a closed-loop test rig, at least one transmission shaft connecting said first and second assemblies.
On such a conventional test rig, the casing of the power transmission device that is to be tested which, when mounted on the test rig, is fixed to an immobile support is secured to a fixed frame of reference which is taken as reference. In addition, said first and second coupling means are designed to take into consideration and compensate, in particular, the imperfections in the manufacture, the integration faults and the deformations caused by the various forces acting on the power transmission device. The loading pattern is introduced in a frame of reference that is rotating on the output shaft (rotor shaft).
A test rig of this type has numerous disadvantages, in particular:
the need to have first coupling means (for connecting the coupling shaft of said first assembly to the output shaft of said power transmission device) which are highly complex so as to be able to absorb the main positioning faults of the power transmission device, particularly of its casing, with respect to a theoretical frame of reference. These positioning faults are manifested, in particular, in defects of alignment (defects of parallelism and angular misalignments) and differences in length. In addition to being complex, these first coupling means are also heavy and very expensive;
the need to provide a measurement pick-up for measuring the various components of the loading pattern; and
the need to provide a box for introducing forces allowing the forces produced in a fixed frame of reference to be transmitted to the rotating frame of reference (output shaft).
Another source, document WO-99/60362, discloses a test rig of the aforementioned type and which additionally comprises, to support the transmission gearbox that is to be tested, a clamping plate which bears this gearbox and can be driven in rotation, about the rotor shaft (output shaft) of said transmission gearbox by two actuators. These actuators are intended only to correct the angular position (about the direction defined by the rotor shaft) in the plane of the clamping plate of the transmission gearbox so as to compensate for the parasitic rotation thereof, under the effect of the torque applied to the input shaft (or shafts). These known means (clamping plate and actuators) therefore have the purpose of reducing angular misalignments in the input shaft (or shafts) and overloads and damage introduced as a result of these misalignments.
The present invention relates to a closed loop or open loop test rig that makes it possible to overcome the aforementioned drawbacks.
To this end, according to the invention, said test rig for testing a power transmission device, particularly a helicopter transmission gearbox, comprising at least an input shaft, an output shaft and a casing, said test rig comprising:
a first assembly comprising coupling means and a coupling shaft which can be connected, via said coupling means to the output shaft of the power transmission device that is to be tested;
a second assembly which can be connected to the input shaft of the power transmission device that is to be tested;
a position-adjustable support on which the casing of the power transmission device that is to be tested can be mounted; and
controllable adjusting means for adjusting the position of said support,
is notable in that said coupling means are formed in such a way as to be able to produce a rigid and coaxial coupling between said coupling shaft and the output shaft of the power transmission device, and in that said support and said adjusting means are formed in such a way as to bring the casing of the power transmission device, when mounted on said support, into a spatial position such that all the forces and moments likely to be generated on the output shaft are applied to said casing.
Thus, by virtue of the invention, the output shaft of the power transmission device (which is secured to the coupling shaft of said first element of the test rig) becomes the reference, and the adjusting means which act on the position of the power transmission device (via said adjustable support) make it possible to introduce the forces and moments needed for simulation, through the casing of said power transmission device. Said adjusting means therefore not only spatially position said support (and therefore the casing of the power transmission device) to compensate for any defects in positioning, but also introduce a loading pattern which simulates the actual operating conditions. In consequence, the present invention makes it possible to reverse the integration architecture, by comparison with the abovementioned customary solution (casing secured to a fixed frame of reference taken as reference and coupling means intended for compensation).
Hence, said means of coupling (between the coupling shaft and the output shaft) can be produced in a very simple and inexpensive way because they do not have to take into consideration the defects in positioning and the parasitic forces (which are compensated for by the adjusting means), thus making it possible to overcome the aforementioned drawbacks.
It will also be noted that, when a helicopter transmission gearbox is being tested, the control of the mean and dynamic forces in a fixed frame of reference which is implemented by the present invention makes it possible, in particular:
to simulate more simply the operation of the mechanical parts of the helicopter by introducing a complete loading pattern of forces and moments representative of the rotor head loading pattern without having to resort to a mechanical box to transfer forces from the fixed frame of reference to the rotating frame of reference;
to reduce the xe2x80x9ctorque ripplexe2x80x9d. This phenomenon, which is manifested in a cyclic variation of the torque about its mean value, is due to the excitation of the entire dynamic loop by the defects of the moving inertial parts (clearances, imbalances, angular misalignments, defects of parallelism, pitch errors, etc). As the torque ripple observed on test rigs is generally higher than that accepted on the helicopter, it is advantageous to be able to bring it down to a comparable level. Introducing forces via the casing makes it possible to act with effect on the torque ripple; and
to avoid measurements in a rotating frame of reference on the output shaft, thus making it possible to eliminate the measurement pick-up, which is expensive and delicate, and which is needed on customary test rigs.
As preference, said adjusting means adjust the position of said support in such a way as to apply forces and moments along the six degrees of freedom of the casing of the power transmission device to said casing.
Thus, unlike the test rig described in document WO-99/60362 which anticipates actuators intended solely to adjust the angular position about the rotor shaft of the transmission gearbox that is to be tested, the adjusting means of the test rig according to the invention make it possible simultaneously:
to introduce the forces and moments via the casing; and
to position said casing spatially, namely along its six degrees of freedom.
Furthermore, in a preferred, but nonexclusive embodiment, said adjusting means comprise jacks.
The present invention also relates to a test system comprising:
a test rig for testing a power transmission device, particularly a helicopter transmission gearbox; and
a power transmission device which comprises at least an input shaft, an output shaft and a casing, and which is mounted on said test rig.
According to the invention, said test system is notable in that said test rig is of the type described hereinabove.
In a preferred embodiment:
said support is provided with a housing which is able to receive an auxiliary support; and
said test system additionally comprises a removable auxiliary support to which the casing of the power transmission device is fixed and which has a shape suited to said housing of the support of the test rig so that it can be mounted stably on said support.
This last embodiment makes it possible to reduce the operations to be performed and the parts to be changed when replacing a power transmission device that is to be tested with another one, since said support remains on the test rig and only said auxiliary support needs to be changed with the various parts it bears.